This invention relates to a mobile communication system; and more particularly, to a method for measuring a location of a mobile station and a method for performing a handoff using the same in a mobile communication system.
In a code division multiple access (CDMA) mobile communication system, when a mobile station is powered-on, the mobile station performs a synchronization with a CDMA channel for communicating with a base station (BS) begins a search for the pilot channel.
After the mobile station acquires the pilot channel, the mobile station adjusts timing to a corresponding system, using a synchronous channel. Here, the pilot channel of each base station has a different pseudo noise (PN) offset.
When the mobile station, moves from an area that a current BS covers to an area that a new BS covers, in an idle state, it senses another pilot channel signal having a large strength from a sector of the new BS, except for the pilot channel signal from the current BS. If the strength of another pilot channel signal of the new BS is equal to or higher than a predetermined threshold value, the mobile station transmits a pilot strength measurement message (PSMM) relating to the pilot channel signal from the sector of the new BS, to the current BS through a reverse traffic channel.
The current BS establishes a new activated set of the PN offset, based on the PSMM received from the mobile station and if a condition of the handoff is satisfied, then performs a handoff to the new BS.
As can be seen above, to select an activated BS in the conventional way, the strength of the pilot channel signal of base stations each having a different PN offset is used. The pilot channel signal is received from the current BS or the neighboring BS. According to the conventional way, the handoff is performed based on the strength of the pilot channel signal of the base stations each having the different PN offset.
In this case, due to an obstacle of geographical features such as buildings, when the mobile station receives a signal transmitted from a BS geographically close to the mobile station, the strength of which is weaker than that of a signal transmitted from a BS geographically relatively far from the mobile station, the mobile station doesn""t performs the handoff to the close BS but the far BS having a good radio environment. However, after passing the above geographical obstacle, the mobile station performs a handoff to the close BS again.
At this time, while repeating a frequent swap and the handoff, there is a high possibility that a call may be dropped, to thereby provide a problem that a quality of a phone call in an overall system may go down.
It is an object of the present invention to provide a method for measuring a location of a mobile station in a mobile communication system.
It is another object of the present invention to provide a method for performing a handoff using the method for measuring the location of the mobile station in a mobile communication system.
In accordance with an aspect of the present invention, there is provided a method for measuring a location of a mobile station in a mobile communication system, the method comprising the steps of: a) when the mobile station is requested of a pilot strength measurement message (PSMM) by a base station or a handoff is occurred, measuring strengths of pilot channel signals of both an activated set of base stations and a neighbor list set of base stations in specific areas within each sector of each base station; b) transmitting the PSMM to the base station; c) comparing the PSMM, in sequence, with strengths of the pilot channel signals of an activated set of the base stations and a neighbor list set of the base stations which are previously measured and stored in a database; and d) according to a comparison result acquired from the step c), measuring the location of the mobile station.
In accordance with another aspect of the present invention, there is provided a method for performing a handoff in a mobile communication system, wherein a mobile station is located in a desired one of 3 sectors in a cell covered by a base station, i.e., an alpha sector, a beta sector, and a gamma sector, however, a strength of a signal from an undesired sector is larger than that from the desired sector due to an obstacle in the desired sector, the method comprising the steps of: a) when the mobile station is requested of a pilot strength measurement message (PSMM) from a base station or a handoff is occurred, measuring strengths of pilot channel signals of an activated set of base stations and a neighbor list set of base stations in specific areas within each sector of each base station; b) transmitting the PSMM to the base station; c) comparing the PSMM, in sequence, with strengths of the pilot channel signals of an activated set of the base stations and a neighbor list set of the base stations which are previously stored in a database; d) according to a comparison result acquired from the step c), measuring the location of the mobile station; and e) disregarding the handoff to the undesired sector, based on the PSMM and the location of the mobile station measured at the step d).
In accordance with further another aspect of the present invention, there is provided a method for performing a handoff in a mobile communication system, wherein a mobile station is located in an overlapped area where an alpha sector and a beta sector, the beta sector and a gamma sector, or the alpha sector and the gamma sector are overlapped within a base station covering 3 sectors of an alpha sector, a beta sector, and a gamma sector, however, a strength of a signal from an undesired sector is larger than those from the other 2 sectors due to an obstacle in the overlapped area, the method comprising the steps of: a) when the mobile station is requested of a pilot strength measurement message (PSMM) from a base station or a handoff is occurred, measuring strengths of pilot channel signals of an activated set of base stations and a neighbor list set of base stations in specific areas within each sector of each base station; b) transmitting the PSMM to the base station; c) comparing the PSMM, in sequence, with strengths of the pilot channel signals of an activated set of the bas stations and a neighbor list set of the base stations which are previously stored in a database; d) according to a comparison result acquired from the step c), measuring the location of the mobile station; and e) disregarding the handoff to the undesired sector in the overlapped area where two sectors are overlapped, based on the PSMM and the location of the mobile station measured at the step d).